Ultra short wave system



Dec. 27, 1938. w GEORGE ET AL 2,141,242

ULTRA SHORT WAVEVSYSTEM Filed March 26, 1955 INVENTORS RALPH W. GEORGETREVOR Patented Dec. 27,1938

UNITED STATES 2,141,242 ULTRA snon'r WAVE SYSTEM Ralph W. George andBertram Trevor, Riverhead, N. Y., assignors to Radio Corporation ofAmerica, a corporation of Delaware Application March 26, 1935,, SerialNo. 13,038

19 Claims.

This invention relates to improvements in ultra high frequency systems,particularly in systems for receiving ultra high frequency oscillations.

An object of the present invention is to provide a very simple andhighly eificient high fre-' quency system capable of receiving ultrashort waves of the order of one meter and less.

A further object is to provide a heterodyne short wave receiving systemcapable of utilizing with high efficiency multi-electrode electrondischarge devices of the acorn type and other very small thermionictubes.

Another object is to provide an ultra high frequency system whereinthere is obtained efiicient 1 coupling between stages and other elementsof the circuit.

A further object is to provide an ultra short wave'receiver which hashigh frequency stability comparable with crystal control but which dis-20 penses with the use of piezo electric crystals.

In the preferred embodiment of the invention there are employed tunable,low loss concentric transmission line resonators, both for controllingthe frequency of the local heterodyne oscillator and for coupling,respectively, the oscillator and the antenna with the detector and radiofrequency amplifier tubes.

It is known that a properly designed transmission line having uniformlydistributed inductance has low losses and may be used to maintain thefrequency of oscillations generated by an electron discharge devicesystem to a high degree of constancy. The line, in effect, acts like asharply tuned circuit whose reactance changes rapidly with change infrequency. In such a concentric line it is the projection of the innerconductor upon the outer conductor which determines the length of theline.

It is now proposed, in accordance with one feature of the invention, toimploy theline not only for controlling the frequency of the oscillatorbut also .for coupling the oscillator to a stage of the system, such asthe detector. To effect this result there is provided an adjustable tapfrom the inner conductor of the line to the input circuit of thedetector. 7

According to another feature of the invention, two such concentric linesare used for coupling one symmetrical circuit to another-symmetricalcircuit; in this case, a dipole antenna is coupled to the grids of apair of push-pull connected radio frequency amplifier tubes, thecoupling being accomplished by taps which are adjustably movable overthe outer surface of the inner conductor. 1

A further feature lies in the use of two tunable, open-ended, U-shapedresonators (hairpin type) which couple together two stages of thereceiver; namely, the push-pull radio frequency amplifier and thepush-pull connected detector tubes. 5

It is to be understood that while these and other features are hereindescribed with special reference to receiving systems, they are notlimited to use therein, since they are equally applicable totransmitting systems and other high frequency arrangements.

Other objects and features, and their advantages will appear from areading of the following detailed description taken in conjunction withthe accompanying drawing, wherein Fig. 1 illustrates a complete ultrahigh frequency receiving system embodying the principles of theinvention, and Fig. 2 illustrates a modification of the method ofcoupling two symmetrical circuits by means of two concentrictransmission lines.

Referring to Fig 1, there is shown an ultra high frequency heterodynereceiving system comprising, broadly, an antenna A, which is coupledthrough a pair of tunable, low loss, concentric transmission lineresonators I, l to the grids 4, 5 of a pair of push-pull connected radiofrequency amplifier tubes 6, 1 whose output is coupled via tunable,open-ended, U-shaped resonators 8, 9 to the push-pull connected detectortubes In, H A local heterodyne oscillator l2, whose frequency isstabilized by a low loss, concentric line resonator l3, supplies thelocally generated oscillations to the detector tubes In, H in parallel,and intermediate frequency energy produced in the detector tubes isresonated in the output circuit l4, tuned to this frequency, from whichthe energy is supplied to any suitable in.- termediate frequencyamplifier-detector circuit l5 and utilized in a recording device, suchas the headphones l6.

Concentric transmission lines I, I comprise two tunable quarter-wavelength resonators, each consisting of an inner conductor 2 and an outerconductor 3 coupled conductively together at one 15 end and electricallyopen at their other end, the coupled ends of'the two resonators beingadjacent each other and connected to a surface of fixed alternatingpotential, such as ground, as shown. Although the two lines are shownplaced end to end, it will be appreciated that this is merely forconvenience, since they can be placed side by side or in any desiredrelative position. Such aline is characterized by a high reciprocal ofpower factor, i.-e., low loss, and has the advantages of ease of controland stability over conventional coil and condenser resonating circuitsfor ultra high frequencies. Balanced antenna A is loosely coupleddirectly, or inductively (Fig. 2), if desired, or capacitively, to therespective grids 4, 5 of radio frequency amplifier tubes 6, l, by way ofadjustable taps over the inner conductors 2, 2 of the lines I, l, atsuitable points of low impedance.

Concentric lines I, l and line l3 are here each chosen to be a quarterwave length long, electrically, for reasons of reliability andsimplicity but it is to be understood that the length is immaterial tothe practice of the invention, since a relatively long transmission linecapable of accommodating a. plurality of wave lengths may be used. It ispreferred to utilize a concentric line of the type disclosed in UnitedStates application Serial No. 1,489, filed January 12, 1935, Patent No.2,108,895, dated February 22, 1938, and United States Patent No.2,077,800, granted April 20, 1937, both by Fred H. Kroger, wherein theeffective length of the line remains constant irrespective oftemperature fluctuations. Tuning of the concentric line resonators isaccomplished by varying the length of the inner conductors since it isthe profile or projection of the inner upon the outer conductor whichdetermines the length of the line. This tuning may be effected either inthe manner described by Kroger in his Patent No. 2,108,895, supra,wherein a micrometer screw adjustment at the open end of the innerconductor effectively lengthens or shortens the inner conductor, or bymoving a short plug at the open end of the line by means of a shaftextending back through the inner conductor to a fine thread screw andknob arrangement, similar in action to a micrometer. The concentric lineresonators, as well as the open-ended U- shaped resonators, and theirrespective tap clips are preferably gold plated to eliminate corrosionand improve their electrical characteristics.

Self bias for the radio frequency amplifier tubes 6, 1 is obtained bypassing the heater current to all the tubes 6, I, I0, II, and I2 throughthe radio frequency bias resistor 30. The gain of the radio frequencyamplifier stage is controlled by the screen grid potentiometer 3|.

The output circuit of amplifiers 6, 1 comprises a long hairpin orU-shaped line resonator 8 connected to the anodes of tubes 6, 1 whichresonator is inductively coupled to a similar hairpin resonator 9, thelatter being in circuit with the respective grids 11, I8 of detectortubes l0 and H. Hairpin resonators 8, 9 have legs which are eachsubstantially a quarter wave length long. These resonators have beenfound to possess the advantage of enabling a better balance to be had inpush-pull circuits. The anode connections from amplifier tubes 6, 1 andthe grid connections from detector tubes l0 and H, are adjustable overthe lengths of the legs of the respective hairpin resonators 8, 9.Tuning is effected over a limited range by means of condensers l9 and20, each of which in practice comprises two small condenser platesclamped directly to the two sides of the hairpin and near the voltagenodal point at its center. Because of the tuning condensers and thecapacity loading from the tubes connected to the legs of the hairpin,the legs are made physically less than a quarter wave long althoughelectrically the device acts like a quarter wave length resonator.

High frequency oscillator 12 is frequency stabilized by frequencycontrol line resonator I3 connected to the grid 2| of the oscillator byWay of the inner conductor of the line. A tap on this inner conductorfeeds the heterodyne oscillations to the grids l1 and 18 of the detectortubes In and H in parallel, by means of connection 22 which extends froma point of suitable low impedance on line l3 through coupling condenser23 to the voltage nodal point of hairpin 9. In the anode circuit ofheterodyne oscillator l2 there is provided a coil 24 which is adjustedto tune the anode circuit of the oscillator and may, if desired, have avariable capacitance 25 across it for tuning purposes. It has'beenobserved, however, that tuning over a considerable frequency range maybe had by tuning only in the grid circuit of the oscillator l2 andhaving a fixed tuning in the anode circuit. By-pass condenser 32- servesto ground the outer conductor of line l3 without short circuiting theradio frequency bias resistor 30. A more conventional method, of course,would be to ground the outer conductor of concentric line l3 to thecathode and insert the grid current meter A-33 in series with the gridleak and cathode. The method illustrated, however, is preferred since ithas the electrical advantage of not loading line IS with the resistanceof the grid leak.

Suitable bias for the detector tubes 10 and II is supplied throughresistance 26 by the source of energy labeled Bias In the output circuitof detector tubes I0 and H are coil 21 and tunable capacity 28 fortuning the anode circuits to the intermediate frequency produced in thedetector tubes by beating the received signal collected by antenna A andamplified by radio frequency amplifiers 6, I with the oscillationsgenerated by local oscillator l2. Radio frequency by-pass condensers 29,29 connected to the respective anodes of detector tubes Ill and Ilcomprise part of the tuning capacity for the tuned circuit 54. In orderto obtain zero ground lead inductance and prevent the radio frequencycondensers from adding'inductance to the by-pass circuit, it isproposed, in practice, to clamp a separate plate in contact with thegrounded panel of the receiver and adjacent to the dielectric andopposite the ungrounded plate.

The intermediate frequency amplifier and detector circuit shown in boxI5 will not be described herein since any conventional, well knownamplifier, demodulator and audio frequency means may be employed.

It is preferred to employ, in the receiver, vacuum tubes of very smallsize of the type known as the acorn or midget type, wherein theinterlead capacity and the inductance of the leads are considerably lessthan the conventional type. Such tubes are adequately described in thecopending application of Bernard Salzberg, Serial No. 732,028, filedJune 23, 1934, Patent No. 2,030,- 187, dated February 11, 1936, to whichreference is herein made for a complete description thereof.

In one receiver successfully used in practice, the intermediatefrequency employed was five megacycles and the receiver covered a signalfrequency range of approximately 68 to 78 centimeters. These figures, itis to be distinctly understood; are merely illustrative and not to betaken as limiting the invention. Obviously the use of a much higherintermediate frequency is desirable.

Fig. 2 illustrates a manner-of coupling antenna A inductively to the twoconcentric lines I, I instead of' conductively, as shown in Fig. 1.

The features of the invention illustrated and described have beenselected for the purposeofclearly setting forth the principles involved;It will be apparent therefore that the structure 'set forthis entirelyillustrative and not definitive it being susceptible of modification tomeet different conditions encountered'in its use, without-departing fromthe spirit and scope of the invention. As an illustratiomthe two hairpinresonators may be replaced with a pair of concentric line resonatorssimilar to those in'theradio frequency circuit using inductive orcapacitive coupling or combinations of either with conductive coupling.

What is claimed is:

1. In combination, a resonant concentric transmission line having.coupled inner andouter coaxial conductors devoid of concentrated reactance, input and output high frequency circuits,

and individual connections from points intermediate the ends of saidinner conductor to said circuits. g

2. In combination, aresonant concentric transmission line effectivelyone-quarter wave length long at the operating frequency and havingcoupled inner and outer coaxial conductors devoid of concentratedreactance, input and output high frequency circuits, and individualconnections extending from points of low impedanceon said innerconductor intermediate the ends thereof to said circuits. 1

3. In combination, a first resonant concentric transmission line havinginner and outer coaxial conductors coupled together at one end, and asecond similar resonant concentric line, the outer coaxial conductors ofboth said transmission lines being coupled together, an input circuitand an output circuit, a connection from a point intermediate the endsof each inner conductor of said two concentric lines'to saidinputcircuit, and a connection from each inner conductor to said outputcircuit. I

4. Apparatus in accordance with claim 3, characterized in this that saidconnections from said inner conductors to at least one of said circuitscomprise a reactive coupling.

5. In combination, a first resonant-concentric transmission line havinginner and outercoaxial conductors coupled. together at one end, and asecond similar resonant concentric line, the outer coaxial conductors ofboth said transmission lines being coupled together, an input circuitand an output circuit, a connection from a point intermediate the endsof each inner conductor of said two concentric lines to said inputcircuit, and a connection from each inner conductor to said outputcircuit, said connections from said inner conductor to at least one ofsaid circuits comprising an inductive coupling.

6. In combination, a first resonant concentric transmission line havinginner and outer coaxial conductors coupled together at one end, and asecond similar resonant concentric line, the coupled ends of both saidtransmission lines being substantially placed end to end, a connectionfrom ground to said outer conductors, balanced symmetrical input andoutput circuits, and individual connections from points of low impedanceon each inner conductor, intermediate the ends thereof, to said inputand output circuits.

7. A system in accordance with claim 6, characterized in this that saidbalanced input circuit is a dipole antenna and said output circuitcomprises a pair of push-pull connected electron discharge devices.

8. In a high frequency communication system,

tub-shaped tuned circuit comprising apair of conductors openatoneoftheir adjacent ends and connected together at the other of theiradjacent ends, a condenser bridging the'trough of said U-shaped tunedcircuit,-said condenser being located between said trough and a planepassing transversely through the'centers of the conductors of said U,high frequencyapparatus, andindividual connections'from a point on eachconductor of said pair intermediate the open end thereof and said troughto said high frequency apparatus.

9. In a high frequency communication system, a U-shaped tuned circuitcomprising a pair of wires open at one-of their adjacent ends andconnected-together at the other of their adjacent ends, a condenserbridging the trough of said U,

another similarly connected U-shaped tuned circuit, said two U-shapedtuned circuits being .electromagnetically coupled together, an inputcircuit and an output circuit, individual connections from each wire ofone of said tuned circuits, intermediate the ends thereof, to said inputcircuit, and'individual connections from each wire of said other tunedcircuit, intermediate the ends thereof, to said output circuit. I '10. Asystem in accordance with claim 9, characterized in this that said inputand output circuits each comprise a pair of push-pull connected electrondischarge devices, said connections to said input circuit extending tothe control grids of one. pair of said devices, and said connections tosaid output circuit extending to the anodes of said other pair ofelectron discharge devices, 11. In an ultra high frequency radioreceiver, a pair of push-pull amplifier electron discharge devices, anda pair of push-pull detector electron discharge devices, the output ofsaid amplifier devices being coupled to the input of said detectordevices, said output and input each including a U-shaped tuned circuitcomposed of a pair of substantially parallel wires directly andconductively coupled together at one of their adjacent ends, open endedat their other ends and having a condenser connected across said wires,energy supply means connectedto the voltage nodal point of each U-shapedtuned circuit, and connections from the wires of said U-shaped tunedcircuits, intermediate. the. ends thereof,-to said electron dischargedevices.

12. In an ultra high frequency radio receiver, a pair of push-pullamplifier electron discharge devices, and a pair of push-pull detectorelectron discharge devices, the output of said amplifier devices beingcoupled to the input of said detector devices, said output and inputeach including a U- shaped tuned circuit composed of a pair ofsubstantially parallel Wires coupled together at one of their adjacentends, open ended at their other ends and having a condenser connectedacross said wires, a connection from each wire of said U-shaped tunedcircuit to its associated circuit, means for supplying a positivepotential to the voltage nodal point of the U-shaped tuned circuitassociated with the output of said amplifiers, and means for supplying anegative potential together with high frequency oscillations to thevoltage nodal point of the U-shaped tuned circuit associated with theinput of said detectors.

13. A system in accordance with claim 12, characterized in this thatsaid last means includes a local heterodyne oscillator provided with afrequency control concentric transmission line having inner and outercoaxial conductors coupled together at one end, and an adjustable tapconnecting said inner conductor from a point of suitable low impedanceto the voltage nodal point of the U-shaped tuned circuit of saiddetectors.

14:. An ultra high frequency radio receiver comprising a dipole antenna,a first concentric transmission line having inner and outer coaxialconductors coupled together at one end, and a second similar concentricline, the coupled ends of both said transmission lines being placedadjacent each other, a connection from ground to said outer conductors,a pair of electron discharge device amplifiers each having a controlgrid and an anode, a connection from one of said control grids to aninner conductor of one of said lines, and a connection from the othercontrol grid to the inner conductor of said other line, and similarconnections from the arms of said dipole to said inner conductors, anoutput circuit connected to the anodes of said amplifiers, a pair ofpush-pull connected electron discharge device detectors having an inputcircuit, said output and input circuits being coupled together and eachincluding a U-shaped tuned circuit composed of a pair of substantiallyparallel wires directly and conductively coupled together at one oftheir adjacent ends and a tunable condenser connected across said wires,and a connection from each wire of said U-shaped tuned circuit to itsassociated circuit, means for supplying a positive potential to thevoltage nodal point of the U-shaped tuned circuit associated with theoutput of said amplifiers and means for supplying a negative potentialtogether with high frequency oscillations to the voltage nodal point ofthe U-shaped tuned circuit associated with the input of said detectors.

15. In an ultra short Wave heterodyne receiver, an energy collector, anamplifier for the collected energy, a detector comprising a pair ofelectron discharge devices, an input circuit for said detectorcomprising a U-shaped tuned circuit, a heterodyne oscillator, a resonantconcentrictransmission line for controlling the frequency of saidoscillator, and means for connecting said concentric line controlledoscillator in parallel and said amplifier in phase opposition withrespect to the legs of said U-shaped tuned input circuit.

16. In combination, a resonant concentric transmission line havingcoupled inner and outer coaxial conductors, input and output highfrequency circuits, and individual connections conductively connectingsaid inner conductor, intermediate the ends thereof, to said circuits.

17. In combination, in an ultra short wave system, a tuned circuitincluding an open ended U-shaped conductor having an over-all lengthsubstantially one-half wave length long, said U- shaped conductorcomprising a pair of parallel wires connected together at one of theiradjacent ends and open at their other ends, a pair of push-pullconnected electron discharge devices each having a grid, cathode andanode, connections extending from said anodes to points on saidconductor on opposite sides of the center of said conductor andintermediate the ends thereof, a connection from said center to saidcathodes, and circuits respectively coupling together said grids andcathodes.

18. In combination, a resonant concentric transmission line having innerand outer concentric coaxial conductors devoid of concentrated reactancecoupled together at one of their adjacent ends and open ended at theirother adjacent ends, an electron discharge device oscillator having ananode, cathode and grid, a connection from said inner conductor to saidgrid, a grid leak circuit comprising a condenser shunted by a resistancein said connection, and a tuned circuit comprising an inductance coilconnecting said anode and said outer conductor, and means forcapacitively coupling said cathode to said outer conductor whereby saidelectron discharge device oscillator is frequency stabilized by saidconcentrio line.

19. In combination, a first resonant concentric transmission line havinginner and outer coaxial conductors, means devoid of concentratedinductance for coupling said conductors together at one end, and asecond similar resonant concentric line, the outer coaxial conductors ofboth said transmission lines being coupled together, an input circuitand an ouput circuit, a connection from each inner conductor of said twoconcentric lines to said input circuit, and a connection from each innerconductor to said output circuit.

RALPH W. GEORGE. BER'I'RAM TREVOR.

